Observing Black Holes from the Stratosphere: Engineering a Balloon-borne VLBI Station and its Future Prospects

by Mr Mayukh Bagchi (Queen's University)

Monday 27 Apr 2026, 16:00 → 17:00 Asia/Kolkata

A269 (Hybrid)

In 2019, the Event Horizon Telescope (EHT) produced the first image of a supermassive black hole shadow by combining simultaneous observations from radio telescopes across the Earth using a technique called Very Long Baseline Interferometry (VLBI). The EHT is limited by two factors: the diameter of the Earth and atmospheric absorption and phase fluctuations, which worsen rapidly at sub-millimeter wavelengths. A space-based VLBI station would address both, but at an enormous cost. A balloon-borne station floating at ~35 km above 99% of the atmosphere is a much cheaper intermediate step, giving access to higher (sub-millimeter) observing frequencies and improving the UV coverage as the balloon drifts across a campaign.
The Balloon-borne VLBI Experiment (BVEX) launched from Timmins, Ontario on 29 August 2025. BVEX is a K-band (22 GHz) balloon-borne radio telescope, built to demonstrate VLBI between a balloon-borne and a ground-based telescope. The payload pairs a single-sideband heterodyne front-end with a Radio Frequency System-on-Chip (RFSoC) backend that runs a high resolution spectrometer and a VLBI packetizer, streaming baseband data over 100 GbE to an onboard NVMe SSD storage system. Phase stability and timing synchronization are anchored on an ultra stable Oven Controlled Crystal Oscillator (OCXO) housed inside a temperature controlled pressure vessel. Getting millimetre level position and attitude knowledge under stratospheric thermal and mechanical conditions is one of the hardest engineering problems on the platform.
In this talk, I will walk through the instrumental design, flight implementation, and lessons learned from the first BVEX flight, along with the upgrades planned for BVEX 2.0, launching from Brazil in 2027. I will close by outlining the science a station like this could enable when paired with the EHT (230 GHz) and ngEHT (345 GHz and above).